BY R. GREIG SMITH. 395 



The filtrate on cooling deposited microscopic crystals which dried 

 as an Arabian-brown skin on porcelain and which melted at 

 157-159°, showing them to be the osazone of arabinose. The 

 portion insoluble in water melted at 187°. This was again treated 

 with 10 CO. of boiling water. The insoluble portion dried as a 

 yellow powder and melted at 192-193°, the melting point of 

 the osazone of galactose. 



The bacterial gum acids had therefore yielded arabinose and 

 galactose on hydrolysis, from which we must conclude that they 

 contain the arabinan-galactan complex and are of the same nature 

 as the natural gums of the arabin group. 



The gum which was found upon Acacia hinervata was of a very 

 pale yellowish-brown and of a dark brown colour. Portions of 

 the same mass showed both colours. It occurred in hemispherical 

 masses and in tears and had a tough gelatinous consistency which 

 enabled it to be cut without fracture. It dissolved readily in 

 water, and in the absence of particles of bark it formed a clear 

 solution with an acid reaction. The acidity of 100 grms. of gum 

 to litmus paper was equal to 3*27 c.c. of normal acid. 



Although there could be no doubt that the gum contained the 

 arabinan-galactan complex, yet to complete the identity of the 

 bacterial with the natural gum acids the proof was needed. 

 Accordingly a portion of the natural gum was dissolved in water, 

 acidified with hydrochloric acid and treated with alcohol. The 

 gum acids were hydrolysed and the sugars tested by means of 

 their osazones in the manner already indicated, when arabin- 

 osazone and galactosazone were obtained. Furthermore, like the 

 bacterial acids, there is apparently a greater proportion of arabinan 

 than galactan in the complex. 



Summary. — A bacterium was found in pure culture at the 

 place from which the natural gum was exuding. This bacterium 

 in the laboratory formed a gum which behaved to reagents, gave 

 the same oxidation products, and contained the same constituents, 

 viz., arabinan and galactan as the natural gum. The bacterium 

 is thus the producer of the natural gum. 



